If anyone thinks Gillingham or MK is the answer, God knows what kind of deluded question they're asking.
Question is: where is the best place for a professional RL side in the south east to set up shop?
There are currently 5 'London' clubs in the Aviva Premiership (in a league of 12). Of those 5, 3 have had to move outside of the M25 and do not look like they will move back inside it any time soon, 1 of them gets decent crowds at Wembley (£10 tickets) and is moving into an athletics stadium with a 10k capacity. Only 1 pro RU club is thriving in London, Quins which is the most Establishment of all the RU clubs in England. All of which to me says, there is limited demand for indigenous professional club rugby (ie long established RU) within the M25, let alone a 'foreign' species of the sport.
Milton Keynes seems to have an appetite for rugby, there are RL connections in the area and it is a very decent facility. Probably a better bet than either Orient or Gillingham.